Injection Molding
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Excessively Fast Gate Freezing of Polypropylene Injection Mold
Problem Phenomenon
The gate solidifies too early during holding, the holding pressure cannot be transmitted to the inside of the cavity, and shrinkage cavities or depressions appear in the thick-wall sections of the product.
The gate freezing time is shorter than the holding time, and shrinkage compensation is insufficient.
Cause Analysis
(1) The gate size is too small, and the cross-sectional area is insufficient to maintain the melt channel
(2) The mold temperature is too low, and the gate area cools too fast
(3) The melt temperature is too low, and the melt viscosity at the gate is high and solidifies rapidly
(4) The gate shape is designed improperly, such as a pinpoint gate with too small a diameter
(5) The holding pressure is set too low, and the melt flow driving force is insufficient
Solution
(1) Increase the gate size; the gate thickness should be at least 60-70% of the product wall thickness
(2) Appropriately increase the mold temperature to the higher value within the range of 40-90°C
(3) Appropriately increase the melt temperature to the higher value within the range of 200-280°C
(4) Optimize the gate shape, avoid excessively small pinpoint gates, and switch to side gates or fan gates
(5) Increase the holding pressure to increase the driving force of the melt through the gate
Key Takeaway
Excessively fast gate freezing is caused by a small gate size or low temperature; the freezing time needs to be extended by enlarging the gate and increasing the temperature.
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